The present invention relates to a mode discriminating device for discriminating photographing modes in a still video system in which a picture which has been photographed using, for instance, an electronic still camera is reproduced from a magnetic disc.
Electronic still cameras are available which operate in a normal mode, a high-band mode, and in both a normal mode and a high-band mode by switching them back and forth. In an electronic still camera operating in a normal mode, as shown in FIG. 2, the luminance signal of the video signal is frequency modulated with a frequency shift of 1.5 MHz from a sync. tip frequency of 6 MHz to a peak white frequency of 7.5 MHz. In an electronic still camera operating in a high-band mode, as shown in FIG. 3, the carrier (DPSK signal) for the ID signal and the carrier for the color signal are similar to those in the electronic still camera operating in the normal mode. However, the luminance signal is frequency-modulated with a frequency shift of 2.0 MHz between a sync. tip frequency of 7.7 MHz and a peak white frequency of 9.7 MHz. Thus, in the high-band mode, the horizontal resolution is higher and the resultant image has a higher picture quality than in the normal mode.
In playback of a magnetic disc on which signals have been recorded in one of these two recording modes, it is necessary to detect the recording mode in which the signals have been recorded on the magnetic disc.
Video tape recorders (VTR) can be used in which the normal mode and the high-band mode are provided. The mode discriminating device thereof may be applied to a still video system as shown in FIG. 4.
In FIG. 4, a magnetic head 1 reads a signal from a magnetic disc (not shown). The RF signal thus read is applied to a reproducing amplifier 2, the output of which is applied to band-pass filters 3 and 4. As shown in FIG. 5, the central frequencies of the band-pass filters 3 and 4 are set in the normal mode carrier frequency band whose central frequency is about 7 MHz and in the high-band mode carrier frequency band whose central frequency is about 9 MHz, respectively. Therefore, when the normal mode carrier is reproduced, a smoothing circuit 5 for smoothing the output of the band-pass filter 3 outputs a signal at a predetermined level. In this operation, the output level of a smoothing circuit 6 adapted to smooth the output of the band-pass filter 4 is much lower than that of the smoothing circuit 5. Similarly, when the high-band mode carrier is reproduced, the smoothing circuit 6 provides a signal at a predetermined level, whereas the output level of the smoothing circuit 5 is much lower than that of the smoothing circuit 6. The output levels of the smoothing circuits 5 and 6 are compared with each other in a comparator 7. For instance, when the output level of the smoothing circuit 5 is higher, the comparator 7 outputs a logic level signal "0" and when the output level of the smoothing circuit 6 is higher, the comparator 7 provides a logic level signal "1". When the difference between the carrier levels becomes small in absolute value, a hold control circuit 8 operates to hold the output of the comparator 7, thereby to prevent error in discrimination of the recording mode. Thus, the recording mode can be determined from the output of the hold control circuit 8.
However, the circuit shown in FIG. 4 is disadvantageous in that two band-pass filters are necessary. Thus, a relatively large area is occupied when the resultant device is installed, and it is accordingly unavoidably bulky.